A familiar problem which is associated with a laser-generated screen image, such as a laser-generated television screen image, is the problem known as speckling, a condition which creates small points of sparkling/twinkling optical behavior which can be extremely distracting and unpleasant. The existence of this speckling problem stands somewhat in the way of successful and acceptable utilization of laser-projection technology to create viewable screen images.
Accordingly, the present invention has undertaken as its focus an effort, which has turned out to be an extremely successful effort, to eliminate, substantially completely, this speckling problem. It has done so by proposing a unique form of a relative-motion optical diffusion screen structure—presented herein in the specific form of a rear-projection screen structure—which functions in an extremely simple fashion to de-speckle (i.e., to anti-speckle) a laser-generated rear-projection image with a very high degree of anti-speckling success. This image is one which is forwardly projected in a laser beam along an appropriate optical beam path extending forwardly from a rearwardly disposed laser-imagery source, i.e., such a source which is disposed to the rear of the rear side of the proposed screen structure, with this path effectively including one of several different embodiments of relative-motion optical diffusion structure. It should be understood at this point that, wherever the term “diffusion” is employed herein, this term is intended to refer to optical diffusion.
Fundamentally, and as was just suggested, the invention rests upon the discovery that placement and operation, in the optical projection path lying between a laser-imagery source and the front, image-viewing side of a viewing screen, of at least one of what is referred to herein as a relative-motion optical diffusion screen, or lens, element (called herein a relative-motion optical diffusion structure), effectively removes, from perception in the viewed projection image, any evidence of the above-mentioned, traditional laser speckling problem.
In the description of the present invention, the structure specifically employed within the realm of a screen structure, and the methodology associated with the operation of this structure, are referred to, as indicated above, utilizing the terminology “relative-motion diffusion”. In the description of the present invention, the phrase “relative-motion diffusion” is intended to refer, in its simplest form, to the creation of motion in a diffusion element which lies in the path of laser beam imagery projection so as to move, in a sense generally transversely, relative to what might be thought of as being the projection-path beam “axis” of laser imagery. In other words, this relative-motion concept involves transverse relative motion, across the path of transmission of a laser image beam, of an optical diffusion lens, or screen, element. This relative-motion diffusion approach also includes so moving such a diffusion element additionally in relation to a second, stationary diffusion element which also lies in a laser-image projection path.
The invention further offers as a feature a special, and somewhat different, practice of double diffusion in the projection path of a laser-imagery beam, with respect to which at least one, unitary, double-diffusion-creating structural element is a motion element, the motion in which produces the behavior referred to above as relative-motion diffusion. This double-diffusion element may, in certain applications, augmentively cooperate with one or more additional diffusion elements also disposed in the path of laser-image projection.
While there are various ways, or approaches, in which the structure and methodology of this invention may specifically be implemented, two very successful, and therefore preferred, such approaches are described herein. In one of these approaches, interposed the front, image-viewing side of the screen structure and the employed laser source, are two optical diffusion lenses, or screens, including, slightly spaced apart, a Fresnel lens, or screen, element, which is a relative-motion element, and disposed toward the viewing screen from the Fresnel lens element, a lenticular lens, or screen, element which is fixed in position, i.e., not relatively movable, with regard to a laser-projection beam.
The second especially interesting and herein disclosed embodiment of the present invention involves a single, double-diffusion screen, or lens element, which has two different kinds of diffusion surfaces formed respectively on its opposite faces. One of these diffusion surfaces, and specifically the surface which is the closest to the laser-projection source, is a Fresnel-formed surface. The other surface, which is more closely adjacent the viewing screen side of things, so-to-speak, is formed as a lenticular structure. This entire, unitary, double-diffusion element is itself the element which moves in a relative-motion fashion with respect to the projection path of a laser-imagery beam, and thus provides a structure with respect to which two diffusion surfaces, slightly spaced apart, both move relative to the path of laser-beam projection. This double-diffusion, unitary element may be incorporated in a screen structure which additionally includes an even greater number of non-relative-motion diffusion lenses, or screens, and more will be said about this arrangement in the detailed description of the invention which is set forth below.
With respect to effective relative motion which functions to eliminate, essentially entirely, the laser speckling problem, this motion preferably is a continuous and random motion, occurring in an infinite variety of directions, with each point of motion in a moving diffusion element essentially “orbiting” irregularly about a nominal, stationary position. Motor structure, preferably electrically energized, which is operatively incorporated into the projection screen structure of the invention, is energized in accordance with practice of the invention to create such random, “orbiting” relative motion, which motion is preferably completely non-angular in nature, in the sense that it is not characterized with any sharp transition points, or with any points of motion stoppage.
These and other important features and advantages which are attained by the present invention will now become more fully apparent as the detailed description which follows is read in conjunction with the accompanying drawings.